Orbital destabilization

In Fig. 9.1, orbitals below the dashed reference line are bonding orbitals when they are filled, the molecule is stabilized. The orbitals that fall on the reference line are nonbonding placing electrons in these orbitals has no effect on the total bonding energy of the molecule. The orbitals above the reference line are antibonding the presence of electrons in these orbitals destabilizes the molecule. The dramatic difference in properties of cyclobutadiene (extremely unstable) and benzene (very stable) is explicable in terms of... 

The crystal field energy level diagram for tetrahedral complexes. The d orbitals are split into two sets, with three orbitals destabilized relative to the two others. 

A pjr-djr effect was found also in the silicon derivative in the series p-CICgEEMMes (M = C, Si, Ge, Sn)74. In this case the hyperconjugation minimizes the difference in orbital energy 712-713, where 713 is the phenyl orbital affected by the conjugation, which is stabilizing for the chlorine 3p orbitals, destabilizing for the M empty d orbitals. 

The isomerization, itself, originates from the a complex (B in Figure 3). However the total activation energy depends critically on the relative energy of A and B (Figure 3). An alkyne C=C triple bond binds more efficiently to a transition metal complex than a o C-H bond since the % C-C orbital is a better electron-donor and the 71 C-C orbital a better electron acceptor than the a and a C-H orbitals, respectively. However, the difference in energy between the two isomers is relatively low for a d6 metal center because four-electron repulsion between an occupied metal d orbital and the other n C-C orbital destabilizes the alkyne complex. This contributes to facilitate the transformation for the Ru11 system studied by Wakatsuki et al. 

It is well known that a change in the H—N—H valence angle of NH3 is important for the energy of the mn orbital. In the transition from the pyramidal to planar conformation, this orbital destabilizes appreciably with decreasing contribution of the nitrogen 2s orbital. This is also reflected in the very low ionization potentials of planar amines (see below). 

Crystal field stabilization energy, CFSE. Each electron in a t2g orbital stabilizes a transition metal ion in octahedral coordination by 0.4Ao, whereas every electron in an eg orbital destabilizes it by 0.6Ao. The crystal field stabilization energy, CFSE, represents the algebraic sum of these factors. Cations may have... 

Fig. 1. Energy-level diagram showing the basis of the model. Stabilization of bonding orbital = destabilization of antibonding orbital = /JSy2.

The essence of the Jahn-Teller theorem is revealed here a symmetrylowering deformation breaks an orbital degeneracy, stabilizing one orbital, destabilizing another. Note the phenomenological correspondence to 80 in the previous section. 

For element 115, the 1+ oxidation state should be important, since an electron is added to the spin-orbit destabilized 7p3/2 orbital. Consequently, element 116 should be stable in the 2+ oxidation state. Element 117 has one electron missing in the 7p3/2 shell. Due to the relativistic stabilization of the 7pi/2 shell it should, therefore, be more stable in the 1+ and 3+ oxidation states compared to the lighter homologues, but less stable in the 5+ and 7+ oxidation states. The 1-oxidation state becomes less important in group 17 due to the destabilization of the 7p3/2 orbital (the EA of element 117 is the smallest in the group [20]). For element 118, oxidation states 2+ and 4+ will be more important than the 6+ state because of the relativistically stabilized l n electrons. It was predicted to form compounds with F and even Cl. 

At first we would like to recall a few important conclusions from earlier studies. The electronic structure of the reactant CpML has been discussed by Hofmann and Padmanabhan [22] for various ligands L and M = Co, Rh, and Ir with the extended Huckel method. As shown in Fig. 5, the valence molecular orbitals are m, ma", n -I- l)a, (w -I- l)a", and (n + 2)a orbitals under Cj symmetry. One sees that the m and rm" orbitals are mainly d x yy and orbitals stabilized by interaction with the ir orbitals on L. At somewhat higher energy is the occupied metal-based d orbital, (n + l)a , with a weak M-L antibonding a interaction. The metal-based (m + l)fl" (dj,j) and (n -H 2)a (d y) orbitals are highest in energy, destabilized by interaction with occupied tt orbitals on the Cp ring. In addition, the (n -I- 2)a orbital destabilized by interaction with the a orbital on L. Thus, it... 

Andbondit molecular orbital (antibonding MO) (Sections 1.11, 1.13, and 1.15) A molecular orbital whose energy is higher than that of the isolated atomic orbitals from which it is constructed. Electrons in an antibonding molecular orbital destabilize the bond between the atoms that the orbital encompasses. 

Spin-orbit destabilization p3/2> dj/2 decrease increase decrease... 

Notice the power of the molecular orbital approach. Every electron that enters a bonding molecular orbital stabilizes the molecule or polyatomic ion, and every electron that enters an antibonding molecular orbital destabilizes it. The emphasis on electron pairs has been removed. One electron in a bonding molecular orbital stabilizes half as much as two, so a bond order of one-half is nothing mysterious. 

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